Said network is, for example, a teledistribution network, a closed circuit television network or a community distribution system; it is conventionally provided to transmit audio-visual data coming from various sources, possibly including sources situated outside the control of the station itself.
However, all the audio-visual data transmitted by such a station comes either from signal generating equipments which generally produce only repetitive or identical data or else from signal processing equipments of the receiver or recorder type which provide retransmission immediately or on request of various television broadcasts and programs.
Due to this fact, a station for applying television signals to a cable network is caused to subject the same channel to successive application of recorded programs, broadcast programs and messages which are reproduced, transmitted or generated locally by the processing equipments or generating equipments of said distribution station.
One problem which arises in these stations is how to detect accurately the end of a broadcast coming from a processing equipment in order to start the following broadcast from another processing equipment, in particular when the processing equipment acts as a receiver of a program transmitted by a source over which the distributor station has no control.
Indeed, it is not possible to foresee exactly when a broadcast will end and there may be unforeseeable interruptions which are a nuisance in that they leave users with a blank screen.
To solve this problem, the present invention therefore provides a system for automatically substituting transmissions at a station situated at the head of a cable network.
The invention applies more particularly to cable head television stations of the type equipped with at least one signal processing equipment of the broadcast receiver or recorder type and with at least one television signal generating equipment under the control of the station.
The automatic substitution system includes at least one switch connected by its output to the cable network and by two mutually exclusive inputs to the television signal output of a processing equipment and to the television signal output of a generating equipment so as to be in a position to link the network to one of the other of said equipment and biassed to link the network to the generating equipment in the absence of any specific instruction to the contrary.
The automatic substitution system also includes at least one synchronization detector connected via its input to a television signal output of the processing equipment associated with a switch and via its output to a control input for said switch so that at least the linking of the processing equipment to the cable network is maintained when signals coming from the processing equipment are synchronized.